FREE BOOKS

Author's List




PREV.   NEXT  
|<   24   25   26   27   28   29   30   31   32   33   34   35   36   37   38   39   40   41   42   43   44   45   46   47   48  
49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   >>   >|  
r root-hairs have crept, they have eaten into the marble and left it corroded. The marks will become more distinct if the marble is rubbed with a little vermilion. In order that the processes of solution and absorption may take place, it is necessary that free oxygen should be present. All living things must have oxygen to breathe, and this gas is as needful for the germination of seeds, and the action of roots and leaves, as it is for our maintenance of life. It is hurtful for plants to be kept with too much water about their roots, because this keeps out the air. This is the reason why house-plants are injured if they are kept too wet. A secondary office of root-hairs is to aid the roots of seedlings to enter the ground, as we have before noticed. The root-hairs are found only on the young parts of roots. As a root grows older the root-hairs die, and it becomes of no further use for absorption. But it is needed now for another purpose, as the support of the growing plant. In trees, the old roots grow from year to year like stems, and become large and strong. The extent of the roots corresponds in a general way to that of the branches, and, as the absorbing parts are the young rootlets, the rain that drops from the leafy roof falls just where it is needed by the delicate fibrils in the earth below.[1] [Footnote 1: Reader in Botany. VI. The Relative Positions of Leaves and Rootlets.] 5. _Comparison of a Carrot, an Onion, and a Potato_.--It is a good exercise for a class to take a potato, an onion, and a carrot or radish to compare, writing out the result of their observations. The carrot is a fleshy root, as we have already seen. The onion consists of the fleshy bases of last year's leaves, sheathed by the dried remains of the leaves of former years, from which all nourishment has been drawn. The parallel veining of the leaves is distinctly marked. The stem is a plate at the base, to which these fleshy scales are attached. In the centre, or in the axils of the scales, the newly-forming bulbs can be seen, in onions that are sprouting. If possible, compare other bulbs, as those of Tulip, Hyacinth, or Snowdrop, and the bulb of a Crocus, in which the fleshy part consists of the thickened base of the stem, and the leaves are merely dry scales. This is called a _corm_. The potato is a thickened stem. It shows itself to be a stem, because it bears organs. The leaves are reduced to little scales (eyelids), in the
PREV.   NEXT  
|<   24   25   26   27   28   29   30   31   32   33   34   35   36   37   38   39   40   41   42   43   44   45   46   47   48  
49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   >>   >|  



Top keywords:

leaves

 

scales

 

fleshy

 
plants
 
needed
 

potato

 
carrot
 

compare

 

consists

 

oxygen


marble
 

thickened

 

absorption

 

exercise

 

Potato

 
radish
 

writing

 

observations

 

called

 
result

reduced

 
Footnote
 

fibrils

 

eyelids

 

delicate

 

Reader

 

Botany

 
organs
 

Comparison

 

Rootlets


Leaves

 

Relative

 

Positions

 

Carrot

 

distinctly

 

marked

 

centre

 

attached

 

sprouting

 

onions


Hyacinth

 

veining

 

remains

 

sheathed

 

forming

 

Crocus

 
Snowdrop
 

parallel

 

nourishment

 

action